1. Field
The present invention relates generally to power supply systems, and more specifically to DC power supply management.
2. Background
Most battery powered devices use power supply management to convert the raw battery output voltage to a cleaner, more consistent power source for the active components in the device. Power supply management is often implemented using DC-to-DC converters, so called because they both are supplied with and produce direct current voltage.
One commonly used DC-to-DC converter is the linear regulator. Linear regulators include a transistor that operates in the linear region. Linear regulators produce a very clean output voltage. However, linear regulators maintain the desired output voltage by dissipating excess power as heat. Thus, they are both inefficient and challenging to integrate into a small package in which heat management is difficult.
Another commonly used DC-to-DC converter is the switched-mode power supply (SMPS). A SMPS incorporates a switching regulator which rapidly switches a power transistor between saturation (full on) and cutoff (completely off) with a variable duty cycle. The resulting rectangular waveform is low pass filtered in order to produce a nearly constant output voltage proportional to the average value of the duty cycle. One advantage of SMPS is that they have greater efficiency than linear regulators because the switching transistor dissipates little power as heat in either the saturated state and the cutoff state. However, even after significant filtering, SMPS generate an output voltage which includes a high amplitude, high frequency component called voltage ripple. Another advantage of a SMPS is that it can step up the voltage, meaning that the SMPS can provide an output voltage that is higher than the voltage level of the input voltage. For example, a battery at the input to a SMPS may provide approximately 3 volts while the SMPS provides 5 volt output.
In wireless devices which produce high frequency output signals, the ripple voltage can modulate the radio frequency (RF) output signal which induces undesirable sideband spurs. If sufficiently large, the sideband spurs both decrease the performance of the wireless system and cause the wireless device to violate emission restrictions set by governing bodies, such as the United States Federal Communications Commission (USFCC.)